Tritium (T) dissolves in light water (H2O) as isotopomers of water (T2O, HTO). Tritium (T) is an isotope of hydrogen (H), and is a radioactive element that emits β-rays (electron beams) and has a half-life period of 12.3 years. In addition, tritium ions (T+) have chemical properties similar to those of hydrogen ions (H+). Tritium ions (T+) remain in the body as they are exchanged with hydrogen ions (H+), which constitute DNA in the body of a living being. Tritium ions can be a causative agent of internal exposure and are thus harmful.
The natural abundance of tritium is significantly small (one tritium atom per 1×1018 hydrogen atoms). Tritium is artificially produced at a fission-type nuclear power facility or a nuclear fusion reaction facility. The concentration of tritium in waste water is limited to 60,000 Bq/L (60 Bq/mL), which is the radioactive concentration limit derived from tritium per 1 liter of sample water defined in the Japanese governmental notification for the dose limit and other details under the provisions of the regulations on the installment and operations of commercial power reactors.
High cost, complicated systems are usually needed for separating tritium from water with conventional technologies using their different physical properties including the boiling points of water molecules (H2O) and water isotopomer molecules (HTO, DTO, T2O), mass, or reactivity of hydrogen gas (H2) with high performance platinum catalysts under high temperature conditions. These conventional methods are described, for example, in Vasaru, G., Tritium Isotope separation 1993, CRC Press, Chap. 4-5, Villani, S., Isotope Separation 1976, Am. Nuclear Soc., Chap. 9, Gould, R. F., Separation of Hydrogen Isotopes 1978, Am. Nuclear Soc., Chap. 9.
The inventors of the present application have recently reported that when a manganese oxide having a spinel crystal structure containing hydrogen ions is applied in the form of powder or an electrode to tritium-containing water, tritium can be absorbed from the tritium-containing water into a solid phase of the manganese oxide via ion-exchange of hydrogen ions (H+) and tritium ions (T+), as described in Hideki Koyanaka and Hideo Miyatake, “Extracting tritium from water using a protonic manganese oxide spinel”, Separation Science and Technology, 50, 14, 2142-2146, (2015) and WO 2015/037734. This technique enables chemical separation of tritium from water at room temperature by separating the manganese oxide powder adsorbing tritium from water.